1. Field of the Invention
The present invention relates to a camera viewfinder system and, more particularly, to a viewfinder system for a large camera, employing negatives of 4 .times. 5 or 6 .times. 6 format, for example.
2. Description of the Prior Art
It is known to provide a large camera with a viewfinder of the so-called groundglass type, such as employed in twin lens reflex cameras for example, this type of viewfinder having the advantages that there are no undue problems of parallax and that it is generally possible to accurately determine whether or not a scene which it is desired to photograph is correctly focussed by the taking lens system of the camera. However, such a viewfinder has the disadvantage that, compared to a viewfinder system which permits eye-level viewing, procedure for adjustment of focus is somewhat inconvenient, since it must be effected while the photographer is looking down into the viewfinder system, and it may not always be possible to correctly focus the camera in a short time, as is required in taking action shots for example. Another disadvantage with this type of viewfinder is that if it is required to employ film having rectangular frames, the film frame side which constitutes the base of a photograph, i.e., the horizontal line of a photographed scene, must always be the same, and it is not possible to alternately make the long and short sides of film frames the bases of photographs, as may be required for practical or artistic purposes.
When the camera employed is of the so-called auto-process type, i.e., a camera in which film is in the form of independent film units each of which is processed inside the camera immediately subsequent to exposure thereof and then moved to the exterior of the camera, whereby a completed print is obtained in a very short time, there is the particular problem that, if as is most convenient from the point of view of holding the camera and of support of a film unit exiting from the camera, it is not possible to correctly view a scene in the viewfinder system while a processed film unit is being moved out of the camera, which is inconvenient when it is desired to take photographs in comparatively rapid succession.
Another disadvantage with this type of viewfinder when employed in a large camera is that since the viewing screen employed in comparatively large and other viewfinder elements must be made proportionately large, overall size of the camera tends to be such that the camera is bulky and difficult to handle.
Most of these problems may be avoided by provision of a viewfinder system of the so-called direct vision type, which is mounted on top or side portion of the camera, for example, and permits eye-level viewing so permitting easy and rapid handling of camera controls and also easy change of the camera to or from a horizontal or vertical position, it further being known to provide direct vision viewfinder systems in which focus is adjustable simultaneously with that of a taking lens system. The main problem associated with this type of viewfinder is that of parallax. This problem is particularly severe in a large camera since the viewfinder system is inevitably a considerable distance from the taking lens system located in a generally central portion of the camera to the viewfinder. Problems of making correction for parallax therefore become complicated, and since a large amount of tilting or compensatory inclination of the camera must be effected in order to ensure a photograph of a scene which is framed in a required manner, particularly in taking close-up shots, the correct amount of compensatory inclination is often difficult to determine or sense, particularly for an amateur.
It is of course possible to allow free positioning of a camera and also avoid problems of parallax by provision of a viewfinder system of the single lens reflex type. But since such a type of viewfinder must include a movable mirror portion large enough to prevent exposure of film prior to actuation of a shutter means, in a large camera the viewfinder system as a whole must be large and in particular there are mechanical problems with respect to ensuring that the large, and hence comparatively heavy mirror, is always moved in a required manner. If this type of viewfinder system is provided in an auto-process camera there are further problems of construction and design since mirror actuation means and means for effecting forwarding of exposed film units out of the camera must all be provided is side portions generally to the rear of the camera.
Another disadvantage in conventional viewfinder systems is that since it is required to obtain an erect image at the eyepiece of a viewfinder system, and since if simple lenses only are employed to effect image erection an optical path length cannot be less than a certain minimum, which is at least equal to the combined focal lengths of the objective lens and erector lens means employed in the viewfinder, in order to keep viewfinder size as small as possible it is practice to make use of a roof-angle prism, which is expensive, and unduly increases the weight of a large camera.
It is accordingly a principle object of the invention to provide a viewfinder system which makes it possible to determine whether a scene is correctly focussed by a taking lens assembly and permits free camera-positioning to obtain photographs of scenes framed in a required manner, but is the source of minimum problems of parallax in a large camera.
It is a further object of the invention to provide a viewfinder system for a large camera having a construction which requires use of light, compact and inexpensive element only.